This invention relates to the field of gas concentrators, and in particular to a miniaturized, portable gas concentrator and method of miniaturized gas concentration.
The pressure swing adsorption cycle was developed by Charles Skarstrom. FIGS. 1A and 1B describe the operation of the Skarstrom xe2x80x9cHeatless Dryerxe2x80x9d. In particular, ambient humid air is drawn into the system from an intake port, by a compressor. The pressurized air flows from the compressor through conduit 9 to a switching valve 4. With the valve in the shown position in FIG. 1A, pressurized air passes through conduit 5a to a pressure vessel 6a. The air feeds into the pressure vessel to a flow-restrictive orifice 1a. The effect of the restrictive orifice is to restrict the flow of gas escaping the pressure vessel. As the pressure builds up in the pressure vessel, water vapour condenses on the sieve material 8. Air with reduced humidity passes through orifice 1a to conduit 12. At conduit junction 11, some of the air is extracted for use from gas extraction port 2 while the remainder passes through conduit 13 to restrictive orifice 1b. The less humid air that passes through orifice 1b is used to blow humid air out of the unpressurized vessel 6b, through conduit 5b, through valve 4, to a vent port 7. When valve 4 switches to the position as shown in FIG. 1B, the opposite cycle occurs.
Thus, as valve 4 cycles from the position of FIG. 1A to the position of FIG. 1B, cyclically, there is a gradual reduction of humidity in the air as sampled at port 2. Likewise gases can be separated by adsorbing components of the gas on selective molecular sieves.
From laboratory observations, employing the Skarstrom cycle in the context of an oxygen separator or concentrator, wherein nitrogen is absorbed by molecular sieve beds to incrementally produce oxygen-enriched air, and using a precursor to the concentrator 1 arrangement of FIG. 1, it was observed that miniaturized (in this case nominal xc2xe inch NPT pipe xc3x976 inch long) molecular sieve beds 12 and 14 could only reach a maximum of 30% concentrated or enriched oxygen detected at the gas extraction ports 11. It was thought that this was because the control valve of the laboratory arrangement was switching before all the nitrogen could be vented out of the molecular sieve beds and the exhaust lines. However, measurements showed that the oxygen concentration was higher than normal. Therefore this was not the problem.
It was also observed that there was a lot of airflow coming out of the molecular sieve bed before the molecular sieve bed was completely pressurized. It seemed that the molecular sieve bed was saturated with nitrogen before the bed was finished pressurizing. FIG. 2 diagrammatically represents such a molecular sieve bed 16. Compressed air enters the bed in direction A through inlet passage 16a. A volume of air B is contained within the bed cavity. A proportion of the volume of air C escapes out through an outflow needle valve 18 while the molecular sieve bed pressurizes. It was thought that the volume of air C escaping could be a much larger volume than the volume of air B inside the bed 16. Thus the question became, what happens when the volume of the molecular sieve bed is decreased during miniaturization, but everything else stays the same?
Poiseauille""s Law was used in comparing the old bed volume B to the miniaturized bed volume to calculate the flow of a fluid that passes through a small hole such as needle valve 18 under a pressure difference.             1      )        ⁢          xe2x80x83        ⁢    Q    =                    r        4            ⁡              (                              p            InsideBed                    -                      p            OutsideBed                          )                    8      ⁢      η      ⁢              xe2x80x83            ⁢      L      
Where xe2x80x9cQxe2x80x9d is the fluid flow in meters cubed per second. xe2x80x9crxe2x80x9d is the radius of the small hole. xe2x80x9cPInsideBedxe2x88x92POutsideBedxe2x80x9d is equal to the pressure difference between inside the molecular sieve bed and outside the molecular sieve bed. xe2x80x9cxcex7xe2x80x9d is the fluid viscosity, and xe2x80x9cLxe2x80x9d is the depth of the small hole.
The flow rate, Q, in meters per second multiplied by the time the flow rate occurred is equal to the volume of flow in meters cubed.
V=Qtxe2x80x83xe2x80x832)
The variable for Q in equation 1 in this case is constant so
V=Ktxe2x80x83xe2x80x833)
where K is some constant value.
Using this information to create a comparison of the Flows and Volumes of the original oxygen concentrator""s bed volume to the new bed volume may be described as:             4      )        ⁢          xe2x80x83        ⁢    R    =                                          V            FlowNew                                V            BedVolum                                                                    eNew                          V              FlowOld                                            V            BedVolum                                              eOld            
Since the time to pressurize the molecular sieve bed can be accurately timed using a programmable logic controller (PLC) timer, the following can be stated:             5      )        ⁢          xe2x80x83        ⁢    R    =                                          Kt            New                                V            BedVolum                                                                    eNew                          Kt              Old                                            V            BedVolum                                              eOld            
or             6      )        ⁢          xe2x80x83        ⁢    R    =                                                        Kt              New                                                                          V              BedVolumeOld                                                                                      Kt              Old                                                                          V              BedVolumeNew                                            =                                                      t              New                                                                          V              BedVolumeOld                                                                                      t              Old                                                                          V              BedVolumeNew                                          
The ratio may then be calculated by inserting values using representative values for a prior art bed and a miniaturized bed (in this case xc2xe inch NPTxc3x976 inch long). Thus, for example:             7      )        ⁢          xe2x80x83        ⁢    R    =                              (          1          )                ⁢                  (          0.001885741          )                                      (          7          )                ⁢                  (          0.0000434375          )                      =    6.2  
From this it was concluded that the molecular sieve material of a nominal xc2xe inch NPT pipexc3x976 inch long molecular sieve bed (the example used in equation 7) has approximately 6.2 times the air passing through it during its pressurization cycle than the molecular sieve material of a prior art oxygen concentrator during its pressurization cycle.
As a consequence of the findings of this analysis it was found to be advantageous to pressurize and vent the molecular sieve beds in a different way than the prior art pressure swing adsorption (PSA) technique. In the method of the present invention the bed is mechanically evacuated after being substantially fully pressurized, hereinafter referred to as a gas packet system or method.
The gas, such as oxygen, concentrator of the present invention for enriching a target component gas concentration, such as the oxygen concentration, in a gas flow, includes an air compressor and vacuum pump, an air-tight first container containing a molecular sieve material for adsorbing a waste component gas such as nitrogen, and a second air-tight container containing molecular sieve material for adsorbing the waste component gas. The first container is in fluid communication with the compressor and vacuum pump through a first gas conduit, and the second container is in fluid communication with the compressor and vacuum pump through a second gas conduit. A third gas conduit connects the first and second molecular sieve containers in fluid communication with each other. A fourth gas conduit branches or xe2x80x9cteesxe2x80x9d off or otherwise cooperates, by means of a flow controller, with the third gas conduit to facilitate delivery of the target gas to the end use. For example, the flow controller may be mounted between two valves on the third conduit. A gas flow controller such as PLC or other dedicated electronic circuit controls actuation of valves mounted to the gas conduits. The electronically controlled valves may also work in co-operation with two passive one-way valves to regulate gas flow through the conduits so as to, in repeating cycles:
(a) prevent gas flow between the first and second containers and to allow compressed gas from the compressor into the first container during a first gas pressurization phase, whereby the first container is pressurized to a threshold pressure level to create a gas packet having an incrementally enriched target component gas concentration such as incrementally enriched oxygen-enriched air, while simultaneously evacuating the second container to a threshold vacuum level during a first evacuation phase whereby the second container is evacuated to the threshold evacuation level to remove a vacuum packet wherein a target waste gas such as nitrogen is removed from the molecular sieve of the second container and expelled to atmosphere,
(b) prevent gas flow between either container and the compressor or vacuum pump and allow a regulated, that is defined or quantified amount of gas to flow from the first container into the fourth gas line for delivery of the target component gas such as oxygen enriched air for an end use by an end user, downstream along the fourth gas conduit,
(c) prevent gas flow between either container and the compressor or vacuum pump or between either container and the end use, and allow a packet of enriched gas to flow between the first and second containers from the first container into the second container during an enriched gas packet flow phase, so that the enriched gas packet flows from the pressurized first container to the evacuated second container and,
(d) prevent gas from flowing between the containers and pressurize the second evacuated container by for example simultaneously firstly exposing the second container to atmospheric pressure with a first one way flow control valve which allows the second container to pressurize to atmospheric pressure, that is ambient equilibrium, without use of the compressor; and then, secondly, actuating the compressor to continue to pressurize the second container after ambient equilibrium has been reached with atmospheric air pressure; and simultaneously preventing gas from flowing between the first and second containers while depressurizing the first container by for example simultaneously firstly venting the first container to atmospheric pressure through a second one way flow control valve to allow the first container to reach atmospheric pressure without the vacuum pump and, secondly, actuating the vacuum pump to evacuate the first container below ambient atmospheric air pressure.
The flow controller may be a gas flow splitter, for example a plug having a 0.0135 inch diameter hole, mounted to the third gas conduit for diverting a portion of the gas packet into the fourth gas conduit for delivery of target component gas, such as oxygen, enriched air for an end use, including use by an end user, downstream to the end use.
The gas flow controller may be a processor cooperating with the compressor and vacuum pump so as to shut off the compressor or vacuum pump when gas flow respectively between the compressor or vacuum pump and both the first and second containers is prevented by the valve actuation. The processor and the compressor and vacuum pump may be powered by a battery. The first and second containers, the conduits, the valves, the processor, the compressor and vacuum pump and the battery may be mounted in a housing.
The first and second containers may be elongate hollow conduits. The molecular sieve beds may, where the waste component gas is nitrogen, include Zeolite as the molecular sieve material. The first and second containers may be generally parallel and mounted in the housing in parallel array. They may be spaced apart laterally relative to the length of the containers so as to define a channel therebetween. The processor and the compressor and vacuum pump may be mounted in the channel. A valve and manifold housing may also be mounted in the channel, the valves mounted to the valve and manifold housing. The valve and manifold housing includes interconnecting manifolds for interconnecting the valves to the first and second containers and the compressor and vacuum pump via the gas conduits.
A gas reservoir may be provided, for example formed as part of the valve and manifold housing, in fluid communication with the gas flow splitter. The reservoir is for containing a reserve of, for example, the oxygen-enriched air for delivery to the end use. One of the valves is a demand valve cooperating between the gas line and the reservoir for release of the reserve into the gas line upon a triggering event triggering actuation of the demand valve. In one embodiment, a pressure sensor cooperates with the gas line, and the triggering event is a drop in pressure in the gas line sensed by the pressure sensor. The pressure sensor provides a triggering signal to trigger the actuation of the demand valve upon detecting the drop in pressure, for example to a pre-set lower threshold pressure, below which the pressure sensor provides the triggering signal.
In the embodiments in which the end use is for example oxygen supply to an end user such as a patient, the first and second containers may be elongate and curved along their length so as to conform to a body shape of the end user when the gas concentrator is worn by the end user. In any event, when the end use is oxygen supply to an end user, it is intended that the gas concentrator may be adapted to be worn by the end user.
Thus, the method of the present invention, for use with the gas concentrator described above, which may further include at least one selectively actuable first valve mounted to the first and second gas conduits, selectively actuable second and third valves mounted to the third gas conduit, the flow controller mounted between the second and third valves so as to regulate the cooperation between the third and fourth gas conduits, may be summarized as the steps of, advantageously sequentially, in repeating cycles:
(a) preventing the gas from flowing between the first and second container and allowing compressed gas from the compressor into the first container during a first gas pressurization phase, whereby the first container is pressurized to a threshold pressure level to create a first enriched gas packet having an incrementally enriched target component gas concentration, while simultaneously actuating the vacuum pump to evacuate the second container to a threshold vacuum level during a first evacuation phase whereby the second container is evacuated to the threshold evacuation level to remove a first waste gas packet whereby a target waste gas is removed from the second container and expelled to atmosphere,
(b) preventing the gas from flowing between either of the containers and the compressor or the vacuum pump and allowing a regulated amount of the first enriched gas packet to flow from the first container into the fourth gas conduit for delivery of the target component gas for the end use, downstream along the fourth gas conduit,
(c) preventing the gas from flowing between either of the containers and the compressor or the vacuum pump or between either of the containers and the end use, and allowing the first enriched gas packet to flow between the first and second containers from the first container into the second container during a first enriched gas packet flow phase, whereby the first enriched gas packet flows from the pressurized first container to the evacuated second container,
(d) preventing the gas from flowing between the containers and actuating the compressor to pressurize the second container to the threshold pressure level to create a second enriched gas packet and simultaneously actuating the vacuum pump to de-pressurize the first container during a second evacuation phase and thereby remove a second waste gas packet whereby waste gas is removed from the first container and expelled to atmosphere,
(e) preventing the gas from flowing between either of the containers and the compressor or the vacuum pump and allow a regulated amount of the second enriched gas packet to flow from the second container into the fourth gas conduit for delivery of the target component gas for the end use, downstream along the fourth gas conduit, and,
(f) preventing the gas from flowing between either of the containers and the compressor or the vacuum pump or between either of the containers and the end use, and allowing the second enriched gas packet to flow between the first and second containers from the second container into the first container during a second enriched gas packet flow phase, whereby the second enriched gas packet flows from the pressurized second container to the evacuated first container.
The compressor and the vacuum pump may advantageously be a combined compressor/vacuum pump in a single unit so that the pressurization and evacuation are accomplished simultaneously by a single device.
The passive first and second one-way valves may be mounted in parallel to the compressor and the vacuum pump respectively so as to be in fluid communication with the first and second gas conduits when the compressor and the vacuum pump are respectively in fluid communication with the first and second gas conduits so that in-flow of gas from external to the concentrator during the first or second pressurization phase is simultaneously assisted by the first one-way valve, and so that out-flow of gas from the concentrator during the first or second evacuation phase is simultaneously assisted by the second one-way valve. Thus, during the first and second evacuation phases, the method may include firstly allowing de-pressurization to equivalent to the ambient pressure external to the concentrator through the second one-way valve and then actuating the vacuum pump to continue de-pressurization, and, during the first and second pressurization phases, firstly allowing pressurization to equivalent to the ambient pressure external to the concentrator through the first one-way valve and then actuating the compressor to continue pressurization.